1. Field of the Invention
This invention relates to flow control valves, and in particular to a bidirectional hydraulic flow control valve.
2. Discussion of the Prior Art
Hydraulic valves capable of regulating high pressure and/or high flow rates in either direction through them are known. Typically, to achieve the desired degree of control with relatively high pressures or flow rates, bidirectional flow control valves have been two stage. Thus, the main stage of the valve was controlled by a hydraulic pressure which was capable of exerting a high force on the main stage spool so as to positively locate it in the desired position, and resist the flow forces through the valve. However, this required the pilot stage of the valve, which was typically controlled by an electro-magnetic coil, to generate the relatively high hydraulic forces needed for positively controlling the main stage spool.
These two stage bidirectional flow control valves were relatively heavy, bulky and expensive. In certain applications, such as in the application of a bypass valve in an automotive power steering system, the size and weight of bidirectional flow control valves made them undesirable. Thus, a need exists for a smaller, lighter and less expensive flow control valve.